The Molecular Imaging Branch (MIB) has been established recently under the direction of Dr Robert Innis with the principal aim of exploiting positron emission tomography (PET) as a brain imaging technique for the investigation of neuropsychiatric disorders. PET is essentially a quantitative and kinetic radiotracer technique. Fundamental to the aim of the MIB is the development of novel positron-emitting radiotracers that can be used with PET to deliver specific biochemical information about the living human or animal brain (e.g. regional neuroreceptor concentration, neurotransmitter synthesis, enzyme concentration, regional metabolism). The PET Radiopharmaceutical Sciences Section is being established to fulfill the need for concerted effort on PET radiotracer discovery. The first phase of laboratories (4000 sq ft) were completed in August 2002. These laboratories incorporate six radiochemistry 'hot-cells', an organic synthesis laboratory, an analytical laboratory and NMR room. The hot-cells are being fitted out with mainly commercial apparatus (PETrace MeI System, Synthia devices and Nuclear Interface radiofluoridation apparatus) for automated radiochemistry with the two major positron-emitters, carbon-11 (t1/2 = 20 min) and fluorine-18 (t1/2 = 110 min), produced by the nearby cyclotrons of the Clinical Center PET facility. The production of [11C]methyl iodide as an important labeling agent and [18F]FECNT as a radiotracer for the dopamine transporter have commenced. The other laboratories are now fully functional and incorporate major equipment for synthesis and analysis, such as flash chromatography, LC-MS, GC-MS, HPLC and 400 MHz multinuclear LC-NMR. A scientific program is being established with focus on developing novel radiotracers for several brain receptors (e.g. cannabinoid, serotonin, NMDA, CRF), neuroreceptor transporters (NET, SERT) and amyloid protein deposits. Research aimed at advancing the power of PET radiochemistry for generic value is also being addressed by investigations of polymer-supported reactions, the exploration of microwave enhanced radiochemistry and the investigation of the potential of micro-reactors. A second phase of laboratories (2000 sq ft), which will expand the facility for organic synthesis, radiochemistry and biological studies in vitro and in vivo, is planned for 2004.